The present invention relates to an electrophotographic recording material composed of an electrically conductive support, optionally an insulating interlayer, a photoconductive system composed of at least one layer of organic materials containing a charge carrier-producing compound and a charge-transporting compound, and a radiation-cured transparent protective layer. The invention also relates to a process for the production of the recording material.
In the electrophotographic process for the production of copies, which has been disclosed in U.S. Pat. No. 2,297,691 and is extensively used today, thorough cleaning of the photoconductive layer is always necessary after transfer to the copy carrier of the toner image which has been developed on the photoconductive layer by a dry process. The cleaning is effected as a rule by brushing or wiping the photoconductive layer with brushes or fabrics suitable for this purpose. In copying machines which operate with liquid developers, the action of the mechanical cleaning is frequently reinforced by concomitant use of a cleaning fluid. The cleaning operations have a damaging effect on the photoconductive layer. Further damaging effects are caused, for example, by the dry developer and by the developer station (countervoltage), and by the action of the developer liquid during developing by liquids. The photoconductive layer is also exposed to the ionized air produced in the charging station. It is known that the required cleaning processes and the other influences mentioned lead to an adverse effect on, or even mechanical damage to, the photoconductive layer, and thus result in a reduction of its useful life.
Photoconductive layers protected with an additional top layer are known. Among these may be mentioned, for example, electrophotographic recording materials according to German Patent Application No. P 30 32 773.2 (U.S. Pat. No. 4,387,148), which have an electrically conductive support and thereon a photoconductor layer which is based on organic or inorganic substances. On top of these a protective layer of radiation-cured, crosslinked polyester is located. The disadvantage of these recording materials is that they comprise, as the photoconductive layer, for example, less flexible selenium or selenium-containing layers in which a curing action by UV irradiation can even cause an undesired gradual modification change. It is also disadvantageous that photoconductor layers are used which are generally less sensitive photoconductor systems and are adversely affected as regards their photoconductor properties by the top layer applied.
Furthermore, German Patent Application No. P 30 32 774.3 (U.S. Pat. No. 4,390,609) discloses a recording material which possesses a protective layer composed of a binder which is resistant to surface abrasion and is composed of a polyurethane resin, a polycarbonate resin, a phenoxy resin, a polyacrylate or polymethacrylate resin, or the most diverse acrylate or epoxide resins containing hydroxyl groups and polyisocyanate groups. The binders employed do not crosslink, or can be subsequently crosslinked thermally, or are self-crosslinking. The protective layers are applied onto the photoconductor layer by coating or immersion, or even by spraying, which may be electrostatic, with subsequent drying and, if appropriate, curing. For this purpose solvents are required which, on the one hand, readily dissolve the substances to be applied, but do not attack or initially dissolve the substances of the particular photoconductor layer.
However, depending on the choice of solvent, the technique of application and the composition of the layer, it has been found that the photoconductive layer located under the protective layer is initially dissolved to various extents, and its photoconductive properties can be disadvantageously affected thereby.